Normal development of ovarian follicles is critical for female reproduction and endocrine function, as it prepares and provides healthy and fertilizable eggs and ensures normal production of steroid and peptide hormones. This process is finely regulated by various intrinsic and endocrine factors. Factors produced by granulosa cells include the TGF-beta superfamily member activin and the steroid hormone estrogen, both of which have been demonstrated to play an intra-ovarian role in regulating ovarian follicle development. I have revealed a linkage between activin and estrogen signaling pathways in the ovary. Mice treated neonatally with activin show an increase in follicle formation and activin stimulates mouse granulosa cell proliferation in vitro. The mechanisms that mediate these events are not known. I have identified Cyp26b1 as the gene that was most significantly suppressed by activin and confirmed its expression in the postnatal ovary. Cyp26b1 degrades the potent morphogen retinoic acid which has been suggested to regulate ovary development. Therefore, the central hypothesis of this proposal is that activin modulates ovarian follicle development through regulation of gene expression profiles of a subset of targets including ERa, ERP and Cyp26b1. The studies proposed will test this hypothesis through three specific aims. Aim 1 will investigate the mechanism(s) underlying activin regulation of ER expression. This will be accomplished by examining involvement of the activin signaling proteins Smad2/3 in activin stimulation of ER expression, and identifying binding site(s) of Smad protein complexes to the ER promoter and determining their functional importance. Aim 2 will identify novel activin regulated genes in the ovary. This will be accomplished by microarray gene expression profiling using neonatal whole ovary cultures and by further verification of the results with real time RT-PCR. Aim 3 will investigate the roles of C3T326b1 and activin in regulating RA environment in the ovary and how Cyp26b1 and RA may affect ovarian follicle formation and development. Together with these experimental studies, the proposal includes a logical plan for further training and mentoring of the applicant, leading to a successful transition to an independent academic career. PUBLIC RELEVANCE: These proposed studies will increase our understanding on the mechanisms of activin regulation of normal ovarian follicle development, and provide new insights into this important reproductive process and hence fertility control, infertility treatment and human health related diseases including cancer.